Header: truncate long display names, bump sign-out tap target to 44px
Adds min-w-0 on flex parents (without which truncate is a no-op inside
flex), truncate + ellipsis on the display name, and min-h-[44px] on the
sign-out button so the hit area meets Apple HIG's 44px floor on touch
devices. Visual chrome unchanged.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>